Imagesetters and platesetters are used to expose substrates that are used in many conventional offset printing systems. Imagesetters are typically used to expose the film that is then used to make the plates for the printing system. Platesetters are used to directly expose the plates.
For example, plates are typically large substrates that have been coated with photosensitive or thermally-sensitive material layers, referred to the emulsion. For large run applications, the substrates are fabricated from aluminum, although organic substrates, such as polyester or paper, are also available for smaller runs.
Computer-to-plate printing systems are used to render digitally stored print content onto these printing plates. Typically, a computer system is used to drive an imaging engine of the platesetter. In a common implementation, the plate is fixed to the outside or inside of a drum and then scanned with a modulated laser source in a raster fashion.
The imaging engine selectively exposes the emulsion that is coated on the plates. After this exposure, the emulsion is developed so that, during the printing process, inks will selectively adhere to the plate's surface to transfer the ink to the print medium.
Typically, one of two different strategies is used to feed substrates to the imaging engine in the printing system. In the simplest case, an operator manually places individual substrates into a feeder that then conveys the substrates through a feed port to the drum scanner. This approach, however, has some obvious drawbacks, since an operator must be dedicated to feeding the substrates. Moreover, the printing system must be housed within a light-safe environment, if the substrates being used have any sensitivity to ambient light. The alternative approach is to use a substrate manager.
Managers typically house multiple substrate cassettes. Each cassette is capable of holding many substrates in a stack. The substrates are separated by slip sheets that are used to protect plate emulsions from damage. For example, in one common implementation, each cassette holds up to one hundred substrates. The manager selects substrates from one of its cassettes and then feeds the substrates, automatically, into the imaging engine, while removing the slip sheets.
In these designs, cassettes are loaded into the manager on a table. The table is then raised and lowered inside the manager to bring the substrates of a selected cassette into cooperation with a picker that grabs individual substrates and feeds them to the imaging engine.